The primary objective of this proposal is the development of a new fragmentation technique to increase the information content of tandem MS experiments required for protein sequencing and identification. This will be achieved through the interaction of multiply-charged peptide ions, produced by electrospray, with a flow of metastable atoms or molecules. The neutral beam of metastable species will be produced in the discharge type source with an asymmetrical electric field to remove charged particles from the beam. Since the beam of metastable species is neutral, there will be no problem with its introduction inside the quadrupole ion guide, where strong rf fields are present. Electron transfer from high-lying metastable electronic levels to multiply charged peptide cations will fragment preferably N-C(alpha) bonds (similar to electron capture dissociation) preserving labile posttranslational modifications. Combining this fragmentation technique with high performance orthogonal acceleration TOP mass spectrometer will allow using these instruments for high-throughput proteomics applications. [unreadable] [unreadable] [unreadable]